Transient Thermo-Fluid Modeling of Loop Heat Pipes and Experimental Validation

Nishikawara, Masahito; Nagano, Hosei; Kaya, Tarik

doi:10.2514/1.t3888

Cited by 29 publications

(17 citation statements)

References 22 publications

(34 reference statements)

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“…where Pcc is calculated from the temperature of the CC, assumed to be constant, and ΔPlines is calculated from the mass flow rate in the loop, assuming Poiseuille flow in a circular pipe, as presented in Ref. [22].…”

Section:  mentioning

confidence: 99%

Formation of unsaturated regions in the porous wick of a capillary evaporator

Nishikawara

Nagano

Mottet

et al. 2015

International Journal of Heat and Mass Transfer

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The heat and mass transfer in a porous wick within a capillary evaporator were analyzed in three dimensions, using a pore network model to simulate immiscible liquid-vapor flow and phase changes in the capillary structure. Characteristics of the porous structure, such as pore radius distribution, permeability and porosity were obtained from measurements of an actual wick and were included in the calculations. Scenarios involving both a fully liquid-saturated and an unsaturated wick containing liquid and vapor were examined under steady state conditions. The location at which the initial vapor phase was generated was identified based on classical nucleation theory. The transition from a saturated to an unsaturated wick was assessed by modeling the distribution of the liquid-vapor interface, and the wicks were compared based on color 3D renderings of temperature and pressure distributions and meniscus curvatures. The maximum temperature of the unsaturated wick exceeded that of the saturated wick although the area of the liquid-vapor interface in the unsaturated wick was five times that in the saturated wick. Since a distribution of pore radii was considered in these calculations, the interface within the wick was not smooth but exhibited asperity. The distribution of meniscus curvatures in the unsaturated wick was much wider compared with the saturated wick. The results obtained in the case of an unsaturated wick demonstrated the occurrence of the heat pipe effect, induced by a distribution of capillary pressures.

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Section:  mentioning

confidence: 99%

Formation of unsaturated regions in the porous wick of a capillary evaporator

Nishikawara

Nagano

Mottet

et al. 2015

International Journal of Heat and Mass Transfer

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“…1 from Evap. 2 was calculated by Equation (11). where, T vap is the vapor temperature in the evaporator-in this calculation, the vapor line inlet temperature (TC10) is used.…”

Section: Test Results Of the Casementioning

confidence: 99%

Operating Characteristics of Multiple Evaporators and Multiple Condensers Loop Heat Pipe with Polytetrafluoroethylene Wicks

Okutani¹,

Nagano²,

Okazaki³

et al. 2014

JECTC

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This paper presents fabrication and testing of a multiple-evaporator and multiple-condenser loop heat pipe (MLHP) with polytetrafluoroethylene (PTFE) porous media as wicks. The MLHP has two evaporators and two condensers in a loop heat pipe in order to adapt to various changes of thermal condition in spacecraft. The PTFE porous media was used as the primary wicks to reduce heat leak from evaporators to compensation chambers. The tests were conducted under an atmospheric condition. In the tests that heat loads are applied to both evaporators, the MLHP was stably operated as with a LHP with a single evaporator and a single condenser. The relation between the sink temperature and the thermal resistance was experimentally evaluated. In the test with the heat load to one evaporator, the heat transfer from the heated evaporator to the unheated evaporator was confirmed. In the heat load switching test, in which the heat load is switched from one evaporator to another evaporator repeatedly, the MLHP could be stably operated. The loop operation with the large temperature difference between the heat sinks was also tested. From this result, the stable operation of the MLHP in the various conditions was demonstrated. It was also found that a flow regulator which prevents the uncondensed vapor from the condensers is required at the inlet of the common liquid line when one condenser has higher temperature and cannot condense the vapor in it.

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“…Bulk thermal conductivity of PTFE and SS316L are referred to in [2] and [14]. As results of preliminary experiments, measured emissivities of the PTFE and SUS porous media were 0.94 and 0.70.…”

Section: Samplesmentioning

confidence: 99%

Microscale Infrared Observation of Liquid-Vapor Phase Change Process on the Surface of Porous Media for Loop Heat Pipe

Odagiri¹,

Nishikawara²,

Nagano³

2016

JECTC

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Loop Heat Pipe (LHP) performance strongly depends on the performance of a wick that is porous media inserted in an evaporator. In this paper, the visualization results of thermo-fluid behavior on the surface of the wick with microscopic infrared thermography were reported. In this study, 2 different samples that simulated a part of wick in the evaporator were used. The wicks were made by different two materials: polytetrafluoroethylene (PTFE) and stainless steel (SUS). The pore radii of PTFE wick and SUS wick are 1.2 μm and 22.5 μm. The difference of thermo-fluid behavior that was caused by the difference of material was investigated. These two materials include 4 different properties: pore radius, thermal conductivity, permeability and porosity. In order to investigate the effect of the thermal conductivity on wick's operating mode, the phase diagram on the q-keff plane was made. Based on the temperature line profiles, two operating modes: mode of heat conduction and mode of convection were observed. The effective thermal conductivity of the porous media has strong effect on the operating modes. In addition, the difference of heat leak through the wick that was caused by the difference of the material was discussed.

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Transient Thermo-Fluid Modeling of Loop Heat Pipes and Experimental Validation

Cited by 29 publications

References 22 publications

Formation of unsaturated regions in the porous wick of a capillary evaporator

Formation of unsaturated regions in the porous wick of a capillary evaporator

Operating Characteristics of Multiple Evaporators and Multiple Condensers Loop Heat Pipe with Polytetrafluoroethylene Wicks

Microscale Infrared Observation of Liquid-Vapor Phase Change Process on the Surface of Porous Media for Loop Heat Pipe

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